The electronic configuration of Pt (atomic number 78) is:

🧠 The Stability Exception Platinum ($Z=78$) is infamous in atomic structure. It sits in Period 6, where the expected $5d-6s$ energy gap is so small that electrons "relocate" for extra stability. This is the same principle that makes $\ce{Cr}$ or $\ce{Cu}$ exceptions, but slightly more complex.

🗺️ The Baseline Build

1. Preceding Noble Gas: Xenon ($Z=54$).
2. Remaining Electrons: $78 - 54 = 24$.
3. The Shell Fill:
   • $6s^2$: 2 electrons.
   • $4f^{14}$: 14 electrons (Complete).
   • $5d^8$: 8 electrons (Wait!).
4. The "Shift": In heavy metals like Pt, the $5d$ and $6s$ energy levels are nearly degenerate. For Pt, the most stable state actually pulls an electron from $6s$ to $5d$, resulting in $5d^9 6s^1$. Result: $[\text{Xe}] 4f^{14} 5d^9 6s^1$.

⚡ The Group 10 Trap Platinum belongs to Group 10 ($\ce{Ni, Pd, Pt}$).

• $\ce{Ni}$: $3d^8 4s^2$ (Standard)
• $\ce{Pd}$: $4d^{10} 5s^0$ (Anomaly)
• $\ce{Pt}$: $5d^9 6s^1$ (Anomaly) Recognizing that the lower members of this specific group are anomalies helps you avoid the "standard" $d^8 s^2$ traps.

⚠️ Common Traps Option (2) $[\text{Xe}] 4f^{14} 5d^{10}$ is a common "over-simplification" guess. Remember, $d^{10}$ is completely full. If Pt had that, it wouldn't have any valence electrons to form common $+2$ states. The correctly identified anomaly is the $s^1$ configuration.

$\boxed{\text{Answer: (d)}}$